- [Voiceover] Now I would like to talk about DNS Recursion.…DNS Recursion are the steps that DNS uses…to make queries of other DNS servers.…When a query is made to a DNS server…it first checks its own zone to see if it has…information requested by the client.…If it doesn't, the DNS server then queries…other DNS servers to try and find the information…the client was asking for.…

Once the record is found, the DNS server then…passes the result back to the requesting client.…This process is called DNS recursion.…By default, DNS recursion is turned on…in a DNS server.…Unfortunately, DNS recursion can be used…to carry out a denial-of- service…or DOS attack against a DNS server.…What happens in this situation,…an attacker can use DNS recursion to launch…an attack against any DNS servers…that are publicly accessible.…

The attacker carries this out by sending a large number…of queries to the targeted DNS server.…When the DNS server gets hit by…a lot of queries, what happens is that…the DNS server slows down…and it can slow down to the point…